From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 520B6C433ED for ; Thu, 8 Apr 2021 13:19:39 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 96D26610CB for ; Thu, 8 Apr 2021 13:19:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 96D26610CB Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:54224 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lUUZM-0008E5-Hc for qemu-devel@archiver.kernel.org; Thu, 08 Apr 2021 09:19:36 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:56058) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lUUYP-0007oD-Qu for qemu-devel@nongnu.org; Thu, 08 Apr 2021 09:18:37 -0400 Received: from galois.linutronix.de ([193.142.43.55]:45708) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lUUYN-00088D-IB for qemu-devel@nongnu.org; Thu, 08 Apr 2021 09:18:37 -0400 From: Thomas Gleixner DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1617887903; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to; bh=R3zqpOysd+UgmybGo5NkOd2hIbYM3pm4y3c57K63JxA=; b=ENEhqGLkUvzI55KKXqGU3V8xzhqVR+tPxf5r7dyk9yRRI7SeIJIaN/+DxQ813iDUkmIjLx QXwfKUTPMOCVP+lLCwi17wenWjeNHHO6l84WdKAWYuYBJiwUwZzv1LQJOzGOakQDDII6k/ 4IWVByqdeg1hN8nNAFsSHWR7gdBlaZxiKfGDmLKV89Qoy3lNvtUbpEF6mETNPkEkcgWm6E DvOFMMRkRv7wg4kdTCfOcU5LsnEbWohnbfBICbYQFFufPSfVtr6eWVEKsk/vPBqNfIsZ2p NqdHOEo76isPI7/BVR37NPHtV874x2mo9eGmTgOl7RBLvreRzQJP06y2zrtmRg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1617887903; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to; bh=R3zqpOysd+UgmybGo5NkOd2hIbYM3pm4y3c57K63JxA=; b=j0BgA4b2utC5JU1UQGkKE9lOkh/3swaNqVDzrGQ5PbRq2VaxQOjbHjUSPSmzBhoFPBtgM8 5PzstL9LzDhmDHBQ== To: Sean Christopherson , Michael Tokarev Subject: Re: Commit "x86/kvm: Move context tracking where it belongs" broke guest time accounting In-Reply-To: Date: Thu, 08 Apr 2021 15:18:23 +0200 Message-ID: <874kgg29uo.ffs@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain Received-SPF: pass client-ip=193.142.43.55; envelope-from=tglx@linutronix.de; helo=galois.linutronix.de X-Spam_score_int: -43 X-Spam_score: -4.4 X-Spam_bar: ---- X-Spam_report: (-4.4 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_MED=-2.3, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Paolo Bonzini , qemu-devel@nongnu.org, kvm@vger.kernel.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Apr 06 2021 at 21:47, Sean Christopherson wrote: > On Tue, Apr 06, 2021, Michael Tokarev wrote: >> broke kvm guest cpu time accounting - after this commit, when running >> qemu-system-x86_64 -enable-kvm, the guest time (in /proc/stat and >> elsewhere) is always 0. >> >> I dunno why it happened, but it happened, and all kernels after 5.9 >> are affected by this. >> >> This commit is found in a (painful) git bisect between kernel 5.8 and 5.10. > > Yes :-( > > There's a bugzilla[1] and two proposed fixes[2][3]. I don't particularly like > either of the fixes, but an elegant solution hasn't presented itself. > > Thomas/Paolo, can you please weigh in? > > [1] https://bugzilla.kernel.org/show_bug.cgi?id=209831 > [2] https://lkml.kernel.org/r/1617011036-11734-1-git-send-email-wanpengli@tencent.com > [3] https://lkml.kernel.org/r/20210206004218.312023-1-seanjc@google.com All of the solutions I looked at so far are ugly as hell. The problem is that the accounting is plumbed into the context tracking and moving context tracking around to a different place is just wrong. I think the right solution is to seperate the time accounting logic out from guest_enter/exit_irqoff() and have virt time specific helpers which can be placed at the proper spots in kvm. Thanks, tglx